This invention relates to the precipitation of fog and more particularly to the precipitation thereof by EGD (electrogasdynamic) spray systems emitting submicron size charged water droplets.
The airline industry loses hundreds of millions of dollars annually due to airport shutdowns by fog. Even at those airports where fully automatic take off and landing is possible for large commercial flights, the extreme care required for ground movement of planes severely slows scheduled arrivals and departures. Because of the danger and cost that this weather brings, systems for dispersing fog have been proposed.
Warm fogs (above 32.degree. F.) are far more frequent than cold fogs (below 32.degree. F.). What is needed is a technique for fog dispersal that is capable of handling warm or cold fogs. There are two types of warm fogs; radiation (little or no wind), and advection (wind). Seeding these warm fogs with hygroscopic crystals dropped from airplanes was found to be unreliable, so thermal systems were developed.
Thermal systems use jet engines to inject heat into the warm fog over a runway and its approach. Raising the temperature of the fog a few degrees causes the water drops to evaporate, and the range of visibility to increase. Because such systems have limitations and bad side effects, only two such systems have been installed (both in France). Operationally, the systems cause so much turbulence that they must be off while planes land, and only large planes can land safely in the residual turbulence. Thus, the frequency of landings and the types of airplanes are both restricted by the thermal fog dispersion system. The thermal system necessarily consumes large amounts of fuel, and its exhaust pollutes the atmosphere. It would be cost effective only at a few of the world's largest, and busiest airports with frequent fog shutdowns.
Electrostatic precipitation of fog drops, much like cleaning of air of suspended dust in an electrostatic precipitator, has been considered by many investigators. However, it was generally agreed that the installation of electrodes above a runway would be highly impractical. Seeding the fog with electrically charged particles from an airplane was considered as an alternative, but this approach has so many operational difficulties that a ground based system is preferred.
The inventor's U.S. Pat. No. 3,757,491, "Apparatus for Suppressing Airborne Particles", Sept. 11, 1973, incorporated herein by reference, describes apparatus for injecting submicron size charged water droplets into airborne contaminants such as dust and inducing an electrostatic field that causes the thus charged contaminant particles to precipitate. EGD nozzles suitable for use in the practice of this invention are known. One such is disclosed in the inventor's U.S. patent application Ser. No. 310,534, filed Oct. 31, 1981, now U.S. Pat. No. 4,433,003 assigned to the assignee of the present invention, and incorporated herein by reference. Fog suppression by emission of charged particles from an electrogasdynamic (EGD) gun, was described by Chiang, T. K., and Gourdine, M. C., "Field Evaluation of an Electrogasdynamic Fog Dispersal Concept", Part 1, Technical Report, FAA-RD-73-33 Department of Transportation, Federal Aviation Administration, February 1973. This was successfully tested in a fog chamber, J. E. Jiusto, "Laboratory Evaluation of an Electrogasdynamic Fog Dispersal Concept", Technical Report FAA-RD-72-99, Department of Transportation, Federal Aviation Administration August 1972, and also in a small field test in the Panama Canal Zone, Wright, T. and Clark, R., "Field Evaluation of an Electrogasdynamic Fog Dispersal Concept", pp. 25-26, l and p. A-2, Part 2, Technical Report, FAA-RD-73-33, Department of Transportation, Federal Aviation Administration, February 1973. However, to the inventor's knowledge, no one has deployed, or taught how to deploy, EGD spray guns around an airport such that visibility is maintained to a specified height above the runway and approach, and in winds of various speed.